The subject invention relates to the grafting of ethylenically unsaturated monomers to polyolefin polymers through the use of peroxide initiators. The resulting functionalized polyolefin polymers are useful as modifiers for, inter alia, polyamide resins.
It is known in the art that unsaturated monomers can be grafted to polyolefin polymers by addition of a peroxide initiator and monomer to molten polymer in a reduced pressure zone of a single screw extruder. The resulting grafted polymer shows appreciable degradation evidenced by an increase in the melt flow rate or melt index of the copolymer as compared to the base polymer. For example, U.S. Pat. No. 3,862,265 assigned to Exxon Research and Engineering Co. discloses, as a critical aspect of the process, highly intensive mixing in an extremely short period of time by melting the polymer before adding the monomer and initiator.
In an effort to reduce the degradation of the polymer, U.S. Pat. No. 3,177,269 assigned to Dow Chemical Company, discloses, after adding monomer and peroxide initiator to a molten polyolefin, "malaxing" the mixture in an extruder to such a low degree that no degradation takes place.